Hydropneumatic clamping cylinder



May 12, 1970 .1. NEMETZ 3,511,048

'HYDROPNEUMATIC CLAMPING CYLINDER Filed May 28, 1968 4 Sheets-Sheet 1 May 12, 1970 J. NEMETZ HYDROPNEUMAT I C CLAMPING CYLINDER Filed May 28, 1968 4 Sheets-Sheet 2 m m m y 12, 9 J. NEMETZ 3,511,048

HYDROPNEUMATIC CLAMPING CYLINDER Filed May 28, 1968 I Q 4 Sheets-Sheet 5 y 2, 1970 J. NEMETZ 3,511,048

HYDROPNEUMATIC CLAMPING CYLINDER I Filed May 28, 1968 4 Sheets-Sheet L United States Patent. M

3,511,048 HYDROPNEUMATIC CLAMPING CYLINDER Josef Nemetz, 14 Rochusplatz, 6503 Wiesbaden-Kastel, Germany Filed May 28, 1968, Ser. No. 732,584 Claims priority, application Germany, June 8, 1967,

Int. Cl. F151) 15/ 26; F01b 1/02 US. Cl. 60-545 11 Claims ABSTRACT OF THE DISCLOSURE A pneumatically operated clamping cylinder includes an internal axially slidable assembly which includes at least two independent relatively axially movable elements which, in turn, operate a radially outwardly movable locking element to hold the clamping element in place.

In hydropneumatic clamping cylinders of the prior art, as soon as the pressure cylinder is operated, the differential piston immediately begins to move and transforms the input pressure to a correspondingly higher working pressure which acts upon the working piston. In other words, the only action in the clamping cylinder is a highpressure action. This results in the disadvantage that the ram stroke of such a cylinder cannot be very long, since the pressure transformation can be achieved only at the cost of the stroke length or of the area ratio, as the case may be.

It is the aim of the invention to eliminate this disadvantage,

This aim is achieved substantially by the fact that the overall stroke is composed of a low-pressure travel and a high-pressure travel, the transformation of low pneumatic pressure to high hydraulic pressure taking place in the clamping cylinder when the piston ram is driven by means of the differential piston which cooperates with the piston ram to cause the high pressure to act on locking members which in turn produce a frictional locking action between the inside wall of the cylinder and an expansion lock ring which accompanies the movement of the difierential piston through its low-pressure travel. In one embodiment of the invention all moving parts of the clamping cylinder are combined into a unit by two sleeves contained in the cylinder, the confronting extremities of the sleeves bearing locking cones Which are mounted slidingly on a cylindrical projection of a counter-pressure plate so as to have a limited movement in the direction of the axis. A control valve and a check valve are provided in the locking cone facing the piston ram.

In a further improvement, a control piston is placed in front of the differential piston, and has an aperture through which the compressed air acts only on a reduced area of the differential piston that is of about the same size as the aperture.

In all embodiments, an air cushion is created between the piston ram and a bearing plate, which is formed by a plug which slides sealingly on the shaft of the piston ram and is equipped with a pressure relief valve.

A somewhat modified, very simple embodiment which can be manufactured at low cost consists in making the sleeve, which contains the assembly of moving parts, of a resilient plastic which, in the area of the high-pressure stroke, is pressed into grooves or threads on the inner wall of the cylinder, thereby producing a locking engagement between the sleeve and the cylinder.

A number of embodiments of the invention are represented in the drawings, in which;

FIG. 1 shows a clamping cylinder having a low pres- 3,511,048 Patented May 12, 1970 sure circuit and a high pressure circuit with valve control,

FIG. 2 shows another embodiment without valve control.

FIG. 3 shows a clamping cylinder having no specific expansion locking members.

FIG. 4 shows another design of the clamping cylinder.

The embodiment of FIG. 1 will first be described. In the barrel 2 of the clamping cylinder, a pair of internal cyclinders 2a, 2b, are displaceably contained, the respective ends of the barrel being closed by caps 1 and 16. In the internal cylinder 2a slides the low-pressure piston 4, which is guided sealingly by its stern in the counter-pressure plate 12. Internal cylinder 2a terminates in the expansion lock taper 6, which in turn slidingly receives a projection 12a of the counter pressure plate 12. In like manner, the other expansion lock member 8 slides on the same projection 12a, and forms a continuation of internal cylinder 2b, being sealed against the wall of the clamping cylinder 2. The high-pressure ram 13 slides in internal cylinder 2b. The extremity of internal cylinder 2b is closed by a plug 15. The sealing against the ram 13 is performed by a cufi gasket 40 whose open side faces the high-pressure piston. An over-pressure valve 11 is provided in the plug 15. Furthermore, two valves 9 and 10 operating in different directions are provided in the expansion lock member 8, and the piston 4 is provided with an oil filter screw 3 for admitting fluid into an inner chamber through opening 5, covered by safety ring 30.

The manner of operation of the clamping cylinder is the following: The compressed air enters through the aperture 17, Since there is oil in chamber 21, which is in communication through orifices 23 with the cavity in projection 12a, the entire contents of the clamping cylinder operate as a unit, so that the compressed air pushes internal cylinder parts 2a and 2b as Well as the expansion lock ring 7 ahead of it until the piston ram 13 encounters the workpiece that is to be clamped, and thus forms a solid basis for the operation that follows.

The low-pressure piston 4 now moves in the direction of the high-pressure piston. The pressure which it exercises now acts upon the oil-filled spaces. When the lowpressure piston moves in this way the air escapes from chamber 20 through orifices 22 past expansion lock ring 7 through the opening valve 9 and through passages 14 into the exhaust line 18. The high pressure acting on both of the outer sides of the expansion lock jaws 6 and 8 forces both these members together, so that their tapers act on the expansion lock ring 7, urging the latter tightly against the inner wall of cylinder 2. In this situation the clamping cylinder is locked. While the high-pressure ram 13 is moving as described, chamber 15a acts as an air spring, because when there is pressure in this chamber the cuff gasket is urged tightly against ram 13. Not until the pressure is high enough to open valve 11 can the high pressure piston move any further in the direction of plug 15. This relief valve 11 brings it about that the bias is constant through the entire high-pressure range.

In the return stroke, the compressed air enters through line 18 through the cuff gasket, which now opens, into chamber 15a, so that the ram 13 leaves its clamping position. At the same time, the compressed air coming from orifice 18 passes through passages 14, opens valve 10, and, traveling in a direction opposite that of the advance stroke, enters into chamber 22 and pushes the low-pressure piston 4 back. The air head of the piston is exhausted through passage 17. Upon the movement of the lowpressure piston 4, the high pressure in chamber 21 ceases. The air pressure between the two expansion lock members 6 and 8 forces the latter apart, releasing the expansion lock ring 7, thereby unlocking the internal cylinder from external cylinder barrel 2, so that the two internal cylinder parts 2a and 2b are displaced together with expansion lock ring 7 in the direction of cap 1 as a single unit. At the end of this stroke, the internal cylinder part 2a. enters into the annular chamber 19 of cap 1. The air in this annular chamber is compressed and thus cushions the final movement. The movement of the two expansion clamp tapers 6 and 8 on projection 12a of the counter-pressure plate 12 is limited axially at the one end by a shoulder on this projection, and at the other end by a snap ring 29.

In the embodiment in FIG. 2, the valves in expansion clamp member 8a have been omitted. In order to achieve an equal operation, a plate 24 is fastened to the free end of internal cylinder part 2a. and is sealed against the cylinder barrel 2. This plate has an aperture 25. Into the low pressure piston 4 there is inserted a cylindrical seal 26 which projects slightly outward. This seal seals the differential piston 4 against plate 24. The manner of operation in this design is as follows. When the pressure has reached a certain level at the beginning of the Working stroke so that the product of the pressure times the area enclosed by seal 26 is greater than the force acting on the differential piston plunger due to the bias, differential piston 4 begins to move and at the same time pressure is applied to its entire area. The rest of the operation is the same as in the embodiment of FIG. 1. Also, there is another small modification in the design represented in FIG. 2. Here the expansion lock tapers 6a and 8a are not made in one piece with the two internal cylinders parts, but are separate elements that are sealed against the internal cylinder parts and the projection of the low-pressure piston. Furthermore, recesses 60 are provided on the expansion lock tapers 6a and 8a in order that the friction of engagement between the expansion lock ring 7a and expansion lock members 6a and 8a may be lower than the friction of engagement between the expansion lock ring and the exterior cylinder. Also, in this embodiment a throttling check valve 27 is installed in a known manner in passage 18. The cross section of the air relief grooves 14 is smaller, to the greatest possible extent, than the throttle cross section, so as to retard the loss of pressure between the expansion lock tapers 7a and 8a.

FIG. 3 shows another very simple embodiment, but one which is functionally equivalent to the first two embodiments. Here no expansion lock cones or expansion lock rings are provided. The internal cylinder members 2av and 2b of FIGS. 1 and 2 are here replaced by an internal cylinder 31 which is made of a resilient plastic. In the highpressure area, cylinder 2 has grooves 33, in the shape of a screw thread if desired. In the area of the high-pressure ram 13 and plug 34, the plastic cylinder 31 is reinforced by a metal sleeve 32, which is not subject to deformation. As soon as the differential piston 4 transforms the low pressure into a high hydraulic pressure, the pressure in chamber 15a builds up until the plastic cylinder 31 deforms in the high-pressure area and produces a frictional as Well as positive engagement on grooves 33. This engagement may be frictional only, if desired, if the inside surface of the outer cylinder and the outside surface of the plastic cylinder are made of appropriate materials and are so designed that, when high pressure occurs, the friction between cylinder 2 and cylinder 31 is greater than the force moving the pistons. In this type of design, a plate 24 can again :be used, as represented in the upper crosssectional portion of the drawing, or a spring-loaded catch 3a can be used with practically the same action. The counter-pressure plate 35 is fastened by means of a snap ring 36 to a flange formed on the plastic cylinder 31.

FIG. 4 shows an embodiment that is approximately equivalent to the one in FIG. 1. The control piston 24, however, additionally has a pressure valve 25a along with a correspondingly small aperture 25, so that the differential piston 4 is indirectly pre-controlled. Plug 15 is also different from FIG. 1: in this case the cross section of the air relief grooves can be kept large, so that a rapid unlocking can be accomplished through the check valve 150. The throttling in the working stroke is performed by the nozzle'hole 15a in conjunction with seal 15b. The same action can also be achieved if the nozzle hole 15a and seal 15b are eliminated, by providing a corresponding clearance 15d or an air relief groove. Cylinder parts 28 with the cones 6 and 8 are then constructed the same'as in FIG. 1.

The operation is as follows: when compressed air enters through aperture 17, the entire internal assembly moves until the ram 13 encounters a resistance. Aperture 25, which is covered by seal 26, is of such a size that the differential piston 4 cannot be put into action through aperture 25 alone. Not until the pressure has built up to the point that valve 25a opens does the differential piston 4 receive the full application and go into action. As soon as differential piston 4 is moved away to open seal 26, aperture 25 is released and the compressed air gains complete access through this aperture, to the differential piston 4. The rest of the operation is as described previously.

The systems are also interchangeable with one another. It is also possible for the counter-pressure plate 12 to be affixed to the expansion clamp cone 8 facing the ram 13.

Having described several forms in which the invention may be practiced, it will be evident to those skilled in the art that various modifications and improvements may be made which would come within the scope of the annexed claims.

I claim:

1. In a fluid operated clamping mechanism, the combination including a cylinder, an axially slidable assembly contained therein, said assembly including a pair of relatively axially slidable pistons defining an expansible closed fluid filled chamber there-between, one of said pistons being attached to a ram for clamping an object, the other of said pistons comprising a counter pressure plate, a low-pressure differential piston axially movable in said cylinder and having a stern of reduced diameter slidable in said counter pressure plate, one side of said low-pressure differential piston being in communication with the interior of the expansible chamber, the other side of the low-pressure differential piston being in communication with an actuating fluid, said assembly also including radially expansible locking means for engagement with the inner wall of said cylinder, and means responsive to pressure in said expansible chamber for actuating said locking means when said ram engages with an object to be clamped.

2. The invention defined in claim 1, wherein said axially slidable assembly includes a pair of internal cylinders having opposed end walls, said two relatively axially slidable pistons being slidable respectively in said internal cylinders, said internal cylinders being provided with cooperating conical surfaces for actuating said locking means, said piston comprising the pressure plate being provided with a hollow stem slidably received in the end walls of the internal cylinders and in sealing engagement therewith for providing communication between the spaces in said internal cylinders defined by said end walls and the respective pistons, and means for limiting the relative axial movement of said internal cylinders in one direction.

3. The invention defined in claim 2, wherein said hollow stem and one of said sleeves are in fixed relationship.

4. The invention defined in claim 2, wherein means is provided for admitting said actuating fluid to the space between the end walls of said sleeves and exteriorly of said hollow stem for urging relative axial displacement of the sleeves, one of said sleeves being provided with check valve means for regulating the release of fluid from and admission of fluid to said space.

5. The invention defined in claim 1, wherein a control piston is axially slidably positioned in said cylinder between a source of actuating fluid and said other side of said low-pressure differential piston, said control piston having a bore therethrough, and seal means for confining the area of the differential piston exposed to the actuating fluid when said control piston is in abutting engagement with the difierential piston.

6. The invention defined in claim 5, wherein said seal means is positioned on the face of said diiferential piston for operative engagement with the adjacent end of said bore in the control piston, and said control piston is also provided with pressure actuated valve means for admitting actuating fluid to an area of the diiferential piston other than that in alignment with said bore.

7. The invention defined in claim 2, wherein said sleeve containing said one piston having a ram attached thereto is also provided with a second end wall, said ram slidably projecting through said second end wall in sealing engagement therewith, said second end wall being provided with pressure relief valve means in communication with the space between said second end wall and said one piston.

8. The invention defined in claim 7, wherein means is provided for venting excess actuating fluid from said space between the opposed end walls of said sleeves, said venting means comprising check valve means provided in said second end wall.

9. The invention defined in claim 7, wherein said sleeve containing said one piston is provided with an axially extending exterior passage means for venting actuating 6 fluid from the space between said opposed end walls of the sleeves.

10. The invention defined in claim 9, wherein said cylinder containing the sleeves is provided with an outlet for actuating fluid, said axially extending passage in said sleeve having a smaller cross-section than the cross-section of said outlet.

11. The invention defined in claim 1, wherein said locking means includes a cylindrical resilient sleeve portion in sliding engagement with the inner Wall of said cylinder, a portion of said inner wall being provided with circumferential rib means, said resilient sleeve portion being expansible into locking engagement with said rib means.

References Cited UNITED STATES PATENTS 2,632,425 3/1953 Grover 9215 XR 3,135,171 6/1964 Michalak 92-14 3,208,759 9/1965 Firestone et a1 9262 XR 3,290,919 12/ 1966 Malinak et al. 60-545 XR 3,320,861 5/1967 Johnson et a1. 9218 MARTIN P. SCHWADRON, Primary Examiner L. J. PAYNE, Assistant Examiner US. Cl. X.R. 

